1. Field of the Invention
The subject invention relates to a method of manufacturing a printed circuit board (PCB). Specifically, the subject invention relates to manufacturing a PCB having vias disposed through solder pads.
2. Description of the Related Art
Printed circuit boards (PCBs) are commonly used to support and electrically connect various components of an electrical or electronic circuit. Over the last several decades, these PCBs have become increasingly complex to match the complexity of the circuits they facilitate as well as aggressive size and packaging requirements.
A typical modern PCB now utilizes a plurality of conductive layers separated by non-conductive layers. Interconnection between the conductive layers is often provided utilizing a plated-through hole, commonly known as a via. These vias provide electrical and thermal transfer from one side of the PCB to another. A recent trend in the manufacture of PCBs is the disposition of the vias at the solder pads formed by the conductive layers. This practice is commonly referred to as “via in pad” design.
Via in pad designs are often wrought with difficulties. For instance, un-plugged via holes, as are typically required in hot air soldered level (HASL) finishes, tend to act as a capillary and wick solder away from the component that it is meant to secure. Another difficulty is the contamination of un-plugged via holes with conformal coatings used to protect the surfaces of the PCB. This contamination degrades heat transfer and touch-up operations are often required to remove the conformal coating from the vias.
HASL finishes themselves often provide additional difficulties in PCB circuit operation. For instance, the HASL finish on both sides of the PCB provides a thermal transfer surface that is also electrically conductive. This leads to less efficient thermal transfer. Also, the HASL finish often presents an uneven surface which contributes to soldering defects, particularly with components having a large number of pins, such as a digital signal processor.
Therefore, there is an opportunity to provide a PCB and method of manufacture that addresses these and other concerns.